The present invention relates to a system and method for analysis and feedback of a subject's running style or running technique, in particular to a system and method that automatically provides feedback on a subject's running reactivity.
In the field of running, different theories exist as to the optimal style that should be used for running faster, longer, and/or minimize the risk of injuries. In particular different types of running methods are advocated by different parts of the running community. On the one hand there is the so-called “Pose method” of running developed by Nicholas Romanov. One philosophy behind the Pose running style is that the runner should avoid up- and downward movements as much as possible while running, since this would expend unnecessary energy. On the other hand there is the so-called Bosch and Klomp style of running, also referred to as the “BK method”, developed by Frans Bosch and Ronald Klomp. One philosophy behind the BK method is that a runner can recover part of his expended energy during running by using the elasticity of his body and in particular the muscles and tendons in his leg and foot section. In the BK method, the runner is thus encouraged to “bounce” up and down while running, which is in stark contrast to the Pose method. Further reference material and specifics on these methods can be found e.g. in the books “Dr. Romanov's Pose method for running” and “Running: Biomechanics and Exercise Physiology in Practice” (2005) by Frans Bosch and Ronald Klomp.
Efficiency in running refers to the ratio of the amount of (desired) work done by the athlete to the amount of energy used. To achieve better efficiency it is advantageous to reduce the amount of “wasted” energy and/or to try to recover and reuse part of the expended energy.
“Reactive running” is a term used in running and in particular by the Bosch and Klomp running school. Reactivity refers to the amount of energy that is reused for the purpose of performing useful work, in this case running. Running more reactively means that more expended energy is reused from one step to the next, and running less reactive means that less or no energy is reused and thus is absorbed or cushioned by damping structures in the body.
The “running reactivity” is a measure of how reactive or spring-like/elastic the steps of a user are during a running activity (as opposed to viscous). In terms of running reactivity, the Pose method and BK method are on two extreme points of a scale, wherein the Pose method strives for minimal impact, essentially reducing reactivity (no bounce) utilizing the more viscous behavior of the muscle-tendon unit to reduce impact while the BK method strives for high reactivity (maximum bounce or spring action) utilizing the more elastic behavior of the muscle-tendon unit to return more energy. For a runner it can be advantageous to know on which part of the scale his running style is located. By receiving feedback on his reactivity, the runner can choose and/or adjust his movement e.g. to emphasize or avoid one or the other type of running style, the less reactive style with more viscous behavior of the muscle tendon unit will result in more energy being absorbed, thus lowering impact experienced by the runner, the more reactive style with more elastic behavior will result in more energy being returned to the runner, but the runner may experience higher impact.
Taylor et al. (Am. J. Sports Med June 1990 vol. 18 no. 3 300-309) describe the viscoelastic behavior of the muscle-tendon unit. As with most biological tissues, muscle is thought to act viscoelastically. Therefore, muscle is considered to have both elastic and viscous properties. Elasticity implies that length changes, or deformations, are directly proportional to the applied forces, or loads. Viscous properties are characterized as time-dependent and rate change-dependent, where the rate of deformation is directly proportional to the applied forces. In biomechanics, true elasticity is represented by Hooke's model of a perfect spring and viscous elements are represented by Newton's model of a hydraulic piston, known as a dashpot. Biomechanical models attempt to represent viscoelastic behavior by combining springs and dashpots in various configurations.
A person's running style can in principle be evaluated by a trained observer, e.g. a personal coach, familiar with various running techniques. It is however desirable to more objectively quantify a running style, in particular to measure or determine a running reactivity as a quantifiable property. Systems for automatically deriving some aspects of a subject's movement pattern during a running activity are known in the art. For example, US patent application 2002/0040601 discloses a motion analysis system comprising accelerometers and a tilt sensor that are mounted on a shoe. This known system measures gait parameters to determine a running velocity and distance traveled. A disadvantage of using accelerometers for deriving movement patterns is that the method can become less accurate if the accelerometers are mounted incorrectly and/or if they become disorientated during use, thus requiring constant calibration. Accelerometers are also very vulnerable for disturbances from vibrations, and unstable, incorrect or loose mounting. Accelerometers are limited to measuring the dynamic elements of the body they are in direct contact with (i.e. the shoe or foot of a runner), the more static phases of movement (stance phase in running) cannot be so easily measured utilizing accelerometry.
There is a need for a practical measurement technique for analyzing foot dynamics in particular of its viscoelastic behavior for assessing the running efficiency, risk of injury or comfort of a user. There is a further need for a method that provides objective feedback on a subject's running reactivity, the method using a simple analysis of data provided by straightforward sensor measurements of the subject's movements. There is also a need for a system for providing and analyzing said data, a system that is straightforward to implement, e.g. using simple sensors and equipment, and also provides a comfort and ease of use for the running subject.